With the intention of inhibiting a vehicle shorter in height such as a passenger car or a mini-car from running under the front or rear portion of a vehicle longer in height such as a motor truck, a vehicle longer in height equipped with an underrun protection mounted beneath the front or the rear portion of the frame has been put into practical use.
An underrun protection at least requires enough strength and stiffness to inhibit another vehicle from running under the vehicle mounting thereon the underrun protection. Unfortunately, an underrun protection formed of steel, which has been widely used for a vehicle, leads to increase in weight of the vehicle.
With the above problem in view, an underrun protection has been developed which can ensure requisite strength and stiffness, preventing the weight from excessively increasing. For example, the following Patent Literature 1 discloses an underrun protection formed of aluminum. According to the Patent Literature 1, the disclosed underrun protection satisfies requisite strength and stiffness, preventing the weight from excessively increasing.